Why is the sum of two rational numbers always rational? select from the drop-down menus to correctly complete the proof. let ab and cd represent two rational numbers. this means a, b, c, and d are , and . the sum of the numbers is ad+bcbd , where bd is not 0. because integers are closed under , the sum is the ratio of two integers, making it a rational number.

1) A number is rational if it can be formed as the ratio of two integer numbers:

m = p/q where p and q are integers.

2) then a/b is a rational if a and b are integers, and c/d is rational if c and d are integers.

3) the sum a/b + c/d = [ad + cb] / (cd)

then given that the integers are closed under the product ad, cb and cd are integers, so the sum ad + cb is also an integer.

So, it has been proved that the result is also the ratio of two integer numbers which is a rational number.

Why is the sum of two rational numbers always rational?